Method of Operating An Ultrasound Handpiece

ABSTRACT

A method of operating an ultrasonic handpiece by pulsing the power supplied to the handpiece and varying the type of vibration during the power pulse.

This application is a continuation of U.S. patent application Ser. No.11/207,642, now U.S. Pat. No. ______ which is a continuation-in-part ofU.S. patent application Ser. No. 11/183,591, filed Jul. 18, 2005,currently co-pending, which is a continuation-in-part application ofU.S. patent application Ser. No. 10/916,675, filed Aug. 12, 2004,currently co-pending. This application is also is a continuation-in-partof co-pending U.S. patent application Ser. No. 10/818,314, filed Apr. 5,2004, priority to which is claimed under 35 U.S.C. §120, which claimspriority to U.S. Provisional Application Serial No. 60/555,240, filedMar. 22, 2004, under 35 U.S.C. §119. This application also claimspriority under 35 U.S.C. §119 to U.S. Provisional Application Serial No.60/587,693, filed Jul. 14, 2004.

BACKGROUND OF THE INVENTION

This invention relates to ultrasonic devices and more particularly todevices for tuning and controlling an ophthalmic phacoemulsificationhandpiece.

A typical ultrasonic surgical device suitable for ophthalmic proceduresconsists of an ultrasonically driven handpiece, an attached hollowcutting tip, an irrigating sleeve and an electronic control console. Thehandpiece assembly is attached to the control console by an electriccable and flexible tubings. Through the electric cable, the consolevaries the power level transmitted by the handpiece to the attachedcutting tip and the flexible tubings supply irrigation fluid to and drawaspiration fluid from the eye through the handpiece assembly.

The operative part of the handpiece is a centrally located, hollowresonating bar or horn directly attached to a set of piezoelectriccrystals. The crystals supply the required ultrasonic vibration neededto drive both the horn and the attached cutting tip duringphacoemulsification and are controlled by the console. The crystal/hornassembly is suspended within the hollow body or shell of the handpieceat its nodal points by relatively inflexible mountings. The handpiecebody terminates in a reduced diameter portion or nosecone at the body'sdistal end. The nosecone is externally threaded to accept the irrigationsleeve. Likewise, the horn bore is internally threaded at its distal endto receive the external threads of the cutting tip. The irrigationsleeve also has an internally threaded bore that is screwed onto theexternal threads of the nosecone. The cutting tip is adjusted so thatthe tip projects only a predetermined amount past the open end of theirrigating sleeve. Ultrasonic handpieces and cutting tips are more fullydescribed in U.S. Pat. Nos. 3,589,363; 4,223,676; 4,246,902; 4,493,694;4,515,583; 4,589,415; 4,609,368; 4,869,715; and 4,922,902, the entirecontents of which are incorporated herein by reference.

When used to perform phacoemulsification, the ends of the cutting tipand irrigating sleeve are inserted into a small incision ofpredetermined width in the cornea, sclera, or other location in the eyetissue in order to gain access to the anterior chamber of the eye. Thecutting tip is ultrasonically vibrated along its longitudinal axiswithin the irrigating sleeve by the crystal-driven ultrasonic horn,thereby emulsifying upon contact the selected tissue in situ. The hollowbore of the cutting tip communicates with the bore in the horn that inturn communicates with the aspiration line from the handpiece to theconsole. A reduced pressure or vacuum source in the console draws oraspirates the emulsified tissue from the eye through the open end of thecutting tip, the bore of the cutting tip, the horn bore, and theaspiration line and into a collection device. The aspiration ofemulsified tissue is aided by a saline flushing solution or irrigantthat is injected into the surgical site through the small annular gapbetween the inside surface of the irrigating sleeve and the outsidesurface of the cutting tip.

There have been prior attempts to combine ultrasonic longitudinal motionof the cutting tip with rotational motion of the tip, see U.S. Pat. Nos.5,222,959 (Anis), No. 5,722,945 (Anis, et al.) and No. 4,504,264(Kelman), the entire contents of which are incorporated herein byreference. These prior attempts have used electric motors to provide therotation of the tip which require O-ring or other seals that can fail inaddition to the added complexity and possible failure of the motors.

There have also been prior attempts to generate both longitudinal andtorsional motion without the use of electric motors. For example, inU.S. Pat. Nos. 6,028,387, 6,077,285 and 6,402,769 (Boukhny), one of theinventors of the current invention, describes a handpiece having twopairs of piezoelectric crystals are used. One pair is polarized toproduct longitudinal motion. The other pair is polarized to producetorsional motion. Two separate drive signals are used to drive the twopairs of crystals. In actual practice, making a handpiece using twopairs of crystals resonate in both longitudinal and torsional directionsis difficult to achieve. One possible solution, also described by one ofthe current inventors, is described in U.S. Patent Publication No. US2001/0011176 A1 (Boukhny). This reference discloses a handpiece have asingle set of piezoelectric crystals that produces longitudinal motion,and a series of diagonal slits on the handpiece horn or tip that producetorsional motion when the horn or tip is driven at the resonatefrequency of the piezoelectric crystals. Again, in practice, theresonate frequency of the piezoelectric crystals and the tip or horn didnot coincide, so simultaneous longitudinal and torsional motion wasdifficult to achieve.

When the tip becomes occluded or clogged with emulsified tissue, theaspiration flow can be reduced or eliminated, allowing the tip to heatup, thereby reducing cooling and resulting in temperature increase,which may burn the tissue at the incision. In addition, duringocclusion, a larger vacuum can build up in the aspiration tubing so thatwhen the occlusion eventually breaks, a larger amount of fluid can bequickly suctioned from the eye, possibly resulting in the globecollapsing or other damage to the eye.

Known devices have used sensors that detect large rises in aspirationvacuum, and detect occlusions based a particular pre-determined vacuumlevel. Based on this sensed occlusion, power to the handpiece may bereduced and/or irrigation and aspiration flows can be increased. SeeU.S. Pat. Nos. 5,591,127, 5,700,240 and 5,766,146 (Barwick, Jr., etal.), the entire contents of which are incorporated herein by reference.These devices, however, use a fixed aspiration vacuum level to trigger aresponse from the system. This fixed level is a threshold value basedupon a fixed percentage of the selected upper vacuum limit. The use andeffectiveness of such systems, however, are limited since they do notrespond until that preset vacuum level is reached. In addition, somesurgical techniques require the plugging or occlusion of the tip, andthe occurrence of an occlusion does not necessarily indicate that thetip and/or wound is getting heated sufficiently to create a concern or athermal injury or bum at the wound site.

U.S. Pat. No. 4,827,911 (Broadwin, et al.) and No. 6,780,165 B2(Kadziauskas, et al.) suggests that the risk of a thermal injury can bereduced by delivering the ultrasound energy in pulses of very shortduration follow by a period wherein no energy is delivered to the tip.Such short pulses can help reduce the amount of energy entering the eye,but as the pulses get shorter, there is less time for the feedback loopto establish the optimum frequency. Current ultrasound handpiece tuningsystems use a feedback loop to monitor the operation of the handpieceand continually tune the handpiece to ensure that the stock of the tipremains constant under all loading conditions. See U.S. Pat. No.5,431,664 (Ureche, et al.). Such feedback loops typically take on theorder of 3-5 milliseconds to cycle and automatically adjust theoperating parameters of the handpiece. As a result, with currentsystems, ultrasonic power pulses of less than 5 milliseconds havelimited ability to establish the optimum frequency, but in general,improvements to the tuning algorithm can be achieved for pulse durationsof less than 20 milliseconds.

Accordingly, a need continues to exist for a reliable ultrasonichandpiece that is capable of delivering ultrasound pulses of less than 5milliseconds while remaining in tune.

BRIEF SUMMARY OF THE INVENTION

The present invention improves upon prior art methods of operating anultrasonic handpiece by pulsing the power supplied to the handpiece andvarying the amplitude of the power during the power pulse.

It is accordingly an object of the present invention to provide a methodfor operating a pulsed ultrasound handpiece.

It is a further object of the present invention to provide a method ofoperating an ultrasound handpiece that delivers ultrasound pulses ofless than 5 milliseconds while remaining in tune.

Other objects, features and advantages of the present invention willbecome apparent with reference to the drawings, and the followingdescription of the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the handpiece of the present inventionwith the outer case removed.

FIG. 2 is a perspective view of the ultrasonic horn that may be usedwith the handpiece of the present invention.

FIG. 3 a block diagram of a driving circuit that may be used with thepresent invention.

FIGS. 4 and 5 are graphs illustrating ultrasound power versus time.

DETAILED DESCRIPTION OF THE INVENTION

As best seen in FIG. 1 handpiece 10 that may be used with the method ofthe present invention generally comprises ultrasonic horn 12, typicallymade from a titanium alloy. Horn 12 has a plurality of helical slits,which will be discussed below. A plurality (typically 1 or 2 pairs) ofring-shaped piezoelectric elements 14 are held by compression nut 15against horn 12. Aspiration shaft 16 extends down the length ofhandpiece 10 through horn 12, piezoelectric elements 14, nut 15 andthrough plug 18 at the distal end of handpiece 10. Aspiration tube 16allows material to be aspirated through hollow tip 20, which is attachedto horn 12, and through and out handpiece 10. Plug 18 seals outer shell11 of handpiece 10 fluid tight, allowing handpiece 10 to be autoclavedwithout adversely affecting piezoelectric elements 14. Addition grooves22 for sealing O-ring gaskets (not shown) are provided on horn 12.

As best seen in FIG. 2, horn 12 contains a plurality of spiral slits 24.Preferably, the width of slits 24 is between 2% and 65% of the outsidediameter of horn 12. This, of course, will affect how many slits 24 canbe made on horn 12 (e.g., if slits 24 are 65% of the diameter of horn12, then only one slit 24 may be cut into horn 12). The width of slits24 selected will depend upon the desired amount of torsional movement.The depth of slits 24 in horn 12 preferably is between 4% and 45% of theoutside diameter of horn 12. Slits 24 may have a flat or square cutbottom, but preferably have a rounded or radiused bottom, which areeasier to manufacture. The length of slits 24 preferably is between 8%and 75% of the length of the larger diameter of horn 12. The pitch ofslits 24 preferably is between 125% and 500% of the larger diameter ofhorn 12. By way of example, the inventors have found that one suitableconfiguration of slits 24 on horn 12 with an outside diameter of 0.475inches is a total of eight slits 24, having a width of 0.04 inches, adepth of 0.140 (with a full radius bottom), a length of 0.7 inches and apitch of 1.35 inches gives suitable torsional movement of horn 12without compromising the longitudinal movement of horn 12.

As best seen in FIG. 1, the location of longitudinal and torsional nodalpoints (the points with zero velocity of the respective mode) isimportant for proper functioning of handpiece 10. The torsional node 26preferably is located at the proximal longitudinal node 28, so that thetorsional node 26 and the longitudinal node 28 are coincident, e.g.,both of which are located on plug 18. Handpiece 10 also contains adistal longitudinal node 30 located at reduced diameter portion 32 ofhorn 12.

As best seen in FIG. 3, drive circuit 34 that may be used with handpiece10 of the present invention preferably is similar to that described inU.S. Pat. No. 5,431,664, the entire contents of which being incorporatedherein by reference, in that drive circuit 34 provides a drive signal tohandpiece 10 and tracks the admittance of handpiece 10 and controls thefrequency of handpiece 10 to maintain a constant admittance. However,drive circuit 34 monitors both the torsional mode and the longitudinalmode and controls these modes in handpiece 10 using two different drivefrequencies. Preferably, the torsional drive signal is approximately 32kHz and the longitudinal drive signal is 44 kHz, but these frequencieswill change depending upon the piezoelectric elements 14 used and thesize and shape of horn 12 and slits 24. Although both the longitudinalor the torsional drive signal may be supplied in a continuous manner,preferably the longitudinal drive signal and the torsion drive signalare alternated, so that the drive signal is provided in a desired pulseat one frequency and then switched to the other frequency for a similarpulse, with no overlap between the two frequencies, but no gap or pausein the drive signal. Alternative, the drive signal can be operated in asimilar manner as described, but short pauses or gaps in the drivesignal can be introduced. In addition, the amplitude of the drive signalcan be modulated and set independently for each frequency.

The pause or gap between drive signals can serve various purposes. Onepurpose is to allow for the ultrasound movement of piezoelectricelements 14 and horn 12 to attenuate or stop so that lens fragments canonce again be suctioned to tip 20 and an occlusion reestablished,thereby increasing the holding force on the lens fragment.Reestablishing the occlusion will increase cutting efficiency of thefollowing pulse of ultrasound, whether longitudinal or torsional.Another purpose of the pause or gap between drive signals is to allowfor the ultrasound movement of piezoelectric elements 14 and horn 12 toattenuate or stop prior to the other (either longitudinal or torsional)mode being excited. Such attenuation between drive signals will reduceamount of potential non-linear interactions in the system which cangenerate undesirable heat and lead to premature degradation ofpiezoelectric elements 14 or mechanical failure of the entire assembly.

Alternatively, there can be a slight overlap in the longitudinal andtorsional drive signals. The overlap may provide relatively short timeintervals when the added action of both torsional and longitudinaldisplacements results in especially fast rate of lens emulsification,and yet the overlap is short enough to prevent piezoelectric elements 14from premature degradation or failure of the entire mechanical assemblyas a result of excessive stress.

Yet another alternative if to have both longitudinal and torsional drivesignals overlap completely thus resulting in applying high stress levelsto the lens material when the two signals overlap, and yet leaving apause in between for the occlusion to reestablish itself and allow forvacuum to build-up, thus improving efficiency of the following pulseapplication.

Still another alternative is to apply a continuous longitudinal signalwith a pulsed torsional signal, or vice versa, a continuous torsionalsignal with a pulsed longitudinal signal. Continuous application oftorsional ultrasound does not cause repulsion because tip 20 movement isoriented perpendicular to the direction of the engagement of tip 20 withthe lens, and the pulsed applications of longitudinal ultrasound areshort enough to prevent overheating or mechanical damage topiezoelectric elements 14.

Finally, as discussed above, both the longitudinal and torsional drivesignals can be applied continuously and simultaneously, with theamplitudes of the both signals being selected such that overheating andexcessive mechanical stress on the system is reduced. If such a drivescheme is to be used, two sets of piezoelectric elements 14 arepreferred with the torsional signal being applied to one set, whilelongitudinal signal applied to the other set.

As best seen in FIGS. 4 and 5, typical duty cycle 200 includes power onportion 210 and power off portion 220. By way of example, FIG. 4illustrates a 50% duty cycle 200, meaning that on portion 210 equals offportion 220. The inventor has discovered that the power level (which maybe measured as a percent of the maximum possible stroke or rotation ofthe tip, or as a percentage of the maximum amplitude of the power signaldelivered to piezoelectric elements 14), within on portion 210 may befurther divided into high power portion 230 and low power portion 240.By way of example, high power portion 230 may be at a 60% power leveland low power portion 240 may be at a 10% power level. Such a divisionof on portion 210 allows high power portion 230 to be of extremely shortduration, for example, between 1 millisecond and 5 milliseconds, andpreferably less than 5 milliseconds, while the overall duration of onportion 210 may remain relatively long, for example, 20 milliseconds orgreater. Maintaining a relatively long on portion 210 allows thefeedback loop contained within drive circuit 34 sufficient time to cycleand automatically adjust the operating parameters of handpiece 10.Further, because low power portion 240 encompasses a significantpercentage of on power portion 210, on the order of 75% to 95%,maintaining a relatively long on power portion 210 does notsignificantly increase the heat generated by tip 20. As a result,ultrasonic power pulses of less than 5 milliseconds are possible whilemaintaining the optimum frequency for handpiece 10 while at the sametime, the potential for thermal injury to the eye is reduced.

One skilled in the art will recognize that both high power portion 230and low power portion 240 may be include longitudinal or torsionalvibration of tip 20 in any combination desired. In addition, while FIGS.4 and 5 demonstrate on power portion 210 as having one high powerportion 230 and one low power portion 240, on power portion 210 may befurther sub-divided into multiple high power portions 230 and/ormultiple low power portions 240, serially, alternately or randomly.

While certain embodiments of the present invention have been describedabove, these descriptions are given for purposes of illustration andexplanation. Variations, changes, modifications and departures from thesystems and methods disclosed above may be adopted without departurefrom the scope or spirit of the present invention.

1. A method of operating an ultrasound hand piece, the methodcomprising: producing at least one periodic vibratory pulse comprisingan on portion during which vibrations are present at a hand piece tipand an off portion during which no vibrations are present at the handpiece tip; wherein the on portion further comprises a first, low powertorsional pulse period to avoid repulsion of lens material, followed bya second, high power longitudinal pulse period.
 2. The method of claim 1wherein the on portion is greater than 10 milliseconds.
 3. The method ofclaim 1 wherein the second, high power longitudinal pulse period is lessthan 5 milliseconds.
 4. The method of claim 1 wherein the on portion isof variable duration.
 5. The method of claim 1 wherein the off portionis of variable duration.
 6. A method of operating an ultrasound handpiece, the method comprising: producing at least one periodic vibratorypulse during which vibrations are present at a hand piece tip; whereinthe periodic vibratory pulse further comprises a first, low powertorsional pulse period to avoid repulsion of lens material, followed bya second, high power longitudinal pulse period.
 7. The method of claim 6wherein the on portion is greater than 10 milliseconds.
 8. The method ofclaim 6 wherein the second, high power longitudinal pulse period is lessthan 5 milliseconds.
 9. The method of claim 6 wherein the on portion isof variable duration.
 10. The method of claim 6 wherein the off portionis of variable duration.
 11. A method of operating an ultrasound handpiece, the method comprising: producing at least one periodic vibratorypulse comprising an on portion during which vibrations are present at ahand piece tip and an off portion during which no vibrations are presentat the hand piece tip; wherein the on portion further comprises a first,high power longitudinal pulse period, followed by a second low powertorsional pulse period to avoid repulsion of lens material.
 12. Themethod of claim 11 wherein the on portion is greater than 10milliseconds.
 13. The method of claim 11 wherein the first, high powerlongitudinal pulse period is less than 5 milliseconds.
 14. The method ofclaim 11 wherein the on portion is of variable duration.
 15. The methodof claim 11 wherein the off portion is of variable duration.
 16. Amethod of operating an ultrasound hand piece, the method comprising:producing at least one periodic vibratory pulse during which vibrationsare present at a hand piece tip; wherein the periodic vibratory pulsefurther comprises a first, high power longitudinal pulse period,followed by a second, low power torsional pulse period to avoidrepulsion of lens material.
 17. The method of claim 16 wherein the onportion is greater than 10 milliseconds.
 18. The method of claim 16wherein the first, high power longitudinal pulse period is less than 5milliseconds.
 19. The method of claim 16 wherein the on portion is ofvariable duration.
 20. The method of claim 16 wherein the off portion isof variable duration.
 21. A method of operating an ultrasound handpiece, the method comprising: producing at least one periodic vibratorypulse during which vibrations are present at a hand piece tip, theperiodic vibratory pulse further comprising a high power period and alow power period; wherein the high power period comprises a firsttorsional pulse period to avoid repulsion of lens material, followed bya second, longitudinal pulse period.
 22. A method of operating anultrasound hand piece, the method comprising: producing at least oneperiodic vibratory pulse during which vibrations are present at a handpiece tip, the periodic vibratory pulse further comprising a high powerperiod and a low power period; wherein the high power period comprises afirst, longitudinal pulse period followed by a second, torsional pulseperiod to avoid repulsion of lens material.
 23. A method of operating anultrasound hand piece, the method comprising: producing at least oneperiodic vibratory pulse during which vibrations are present at a handpiece tip, the periodic vibratory pulse further comprising a high powerperiod and a low power period; wherein the low power period comprises afirst torsional pulse period to avoid repulsion of lens material,followed by a second, longitudinal pulse period.
 24. A method ofoperating an ultrasound hand piece, the method comprising: producing atleast one periodic vibratory pulse during which vibrations are presentat a hand piece tip, the periodic vibratory pulse further comprising ahigh power period and a low power period; wherein the low power periodcomprises a first, longitudinal pulse period followed by a second,torsional pulse period to avoid repulsion of lens material.